1. Field of the Invention
The present invention relates to engine mounts for a motor vehicle, and more particularly relates to engine mount bushings used to isolate noise, vibration and harshness felt by a driver of a motor vehicle.
2. Description of the Related Art
In current day automotive vehicles the engine in the vehicle is connected to the frame or body of the vehicle via a vibration control component or unit. The vibration control component generally includes an engine mount bushing used in conjunction with a bracket system. The vibration control components will isolate any engine induced noise and vibration from being transmitted to the passenger compartment of the automotive vehicle. In a typical automotive vehicle the engine is connected to the body of the vehicle using three engine mount components, two load bearing components and one torque reaction component or mount. In more sophisticated vehicles the engine mounting system may utilize up to five engine mount components to improve the noise, vibration and harshness (NVH) performance. The mechanical behavior and characteristics of the bushing, along with the engine mounting brackets and its configuration, directly affects the noise, vibration and harshness felt by the driver through the steering wheel and seat rail. Prior art engine mount bushings generally use rubber as an isolating material. The rubber durometer plays a very important role in determining the isolation characteristics of the prior art bushings.
The vibration control component generally includes an engine mount component that is made from two parts, a rubber isolating bushing and a metal or composite material bracket. The rubber bushing is generally an integral part of the bracket and the two in combination create the isolating member. The engine mount is hard mounted to the sub-frame or body of the vehicle while the bushing core is attached to the engine. It should also be noted that in some instances the engine mount is hard mounted to the engine while the bushing core is attached to the sub-frame or body of the vehicle.
In operation, the conventional rubber bushing, i.e., two legged rubber bushing, is in compression during engine loading and is in tension when the engine is in reverse or rebound. The radius or outer shape of the bushing is determined by the required rates and allowable displacement of the bushing. The main load bearing direction of the bushing is very critical since the rate in this direction effects the noise, vibration and harshness performance considerably. Generally, in the conventional rubber bushings, the overall dimension and size of the rubber legs are the main design parameters along with the size of the ring. Rubber is the material of choice in the conventional bushings. Rubber is an incompressible material that will be displaced during loading which will require a large ring to accommodate the displaced value while maintaining the designed rates. Furthermore, the incompressible rubber material will resist any movement under loading conditions thus resulting in a drastic increase in rate behavior under pre-loaded conditions. The more the rubber element is compressed the higher its stiffness becomes. This rate buildup is almost instantaneous in this type of design. This becomes a very large drawback associated with the conventional rubber bushings since the effective rate varies considerably with the amount of engine pre-load. Therefore, there is a need in the art for an engine mount isolating bushing that provides a more consistent performance level over a wide range of engine loading and temperatures and does not have the large rate variations with the engine pre-load of prior art automotive vehicles.
One object of the present invention is to provide a new engine mount isolating bushing.
Another object of the present invention is to provide a foamed elastomer engine mount isolating bushing.
Yet a further object of the present invention is to provide a new bushing that provides for a much smaller package while maintaining a more consistent performance level over a wide range of engine loads and temperatures.
Still a further object of the present invention is to reduce the component weight while improving durability and noise, vibration and harshness performance issues.
Still a further object of the present invention is to provide a foamed elastomer and elastomer combination bushing.
To achieve the foregoing objects a bushing for use in an automotive vehicle is described. The bushing includes a hard case, and a core within the case. The bushing also includes an elastomer isolator member contacting the core and the case. The bushing further includes a foamed elastomer isolator contacting the core and the case.
One advantage of the present invention is that the new foamed elastomer bushing provides for a much smaller package than the conventional rubber bushings.
Still another advantage of the present invention is the improved consistency of the performance level over a wide range of engine loading and temperature variables.
Yet a further advantage of the present invention is the reduction in component weight while improving on durability and noise, vibration and harshness performance.
Another advantage of the present invention is the reduction in size of the bushing and brackets necessary to connect the bushing to the vehicle body frame and engine.
Yet another advantage of the present invention is the foamed elastomer being pre-compressed which provides for a good isolation from vertical load rate shifts.
Other objects, features, and advantages of the present invention will become apparent from the subsequent description and appended claims, taken in conjunction with the accompanying drawings.